This disclosure relates generally to the field of chemical treatment systems for use with hydrocarbon producing wells. More specifically, the disclosure relates to methods for operating chemical treatment systems which inject chemicals into the well.
In wellbores drilled through subsurface formations and then used for production of hydrocarbons, a pipe or casing may be disposed in the wellbore from the Earth's surface to the bottom of the well. The casing serves to hydraulically isolate the various subsurface formations penetrated by the wellbore and to provide the wellbore with a degree of mechanical stability. Typically a tubing string, which is a pipe of considerably lesser diameter than the casing, is positioned within the well casing. The purpose of the tubing string is to enable produced fluids to move to the Earth's surface at greater velocity than would be possible within the casing. The hydrocarbons, and in many cases a considerable amount of connate water (water naturally present in the pore spaces of the formations), enter the tubing through perforations located adjacent the producting formations, travel through the tubing, to a wellhead at the Earth's surface. In some wells, where the natural fluid pressure in the subsurface formations is not sufficient to lift the produced fluids to the Earth's surface, the fluids may be pumped to the surface with a “sucker rod” pump or with a downhole electrical submersible pump.
At the Earth's surface, various production equipment directs the produced fluids to holding tanks and/or to a pipeline. The production equipment typically comprises tubing, valves, piping, and other components. The produced fluids may contain numerous compounds which adversely affect the production equipment. For example, paraffins and water/oil emulsions can coat well production equipment and can eventually plug off the tubing and/or plug the perforations in the casing. In addition, chemical reactions between the produced fluids and metallic equipment can cause scale to be formed on the well production equipment, and some compounds in the produced fluids can corrode the well production equipment.
Various techniques are known in the art to treat these well conditions to extend the useful life of the well production equipment, tubing and casing. In wells susceptible to paraffin build-up, for example, “treater trucks” or “hot oil trucks” are regularly dispatched to pump heated oil and/or heated water into the well. The heated oil and/or water is pumped into the well through the annular space between the tubing and the casing, travels down through the annulus to melt the paraffin deposits in the well production equipment, and the returns to the surface through the tubing. In wells susceptible to corrosion and scale problems, high pressure injection treater trucks pump batches of chemicals into the well to chemically remove the scale, and to inhibit the causes of corrosion. All of these techniques require regular maintenance services which are costly and which do not continuously treat the well. Treater truck or batch treatment of wells is less efficient than continuous treatments because more chemicals are typically injected in batch treatment operations.
To avoid inefficiencies associated with treater truck maintenance of hydrocarbon producing wells, it is known in the art to use mechanical pumps to inject chemicals into a well. Typically, mechanical pumps are supplied from a storage tank which holds the chemicals. The mechanical pumps and storage tanks are located adjacent the well for several reasons, such as for reducing the length of power cable or piping that connects the pump to a power source such as electricity or natural gas. The tanks are located above the pump and the chemical is gravity fed to the intake port of the pump
Another device known in the art for providing controllable, continuous chemical treatment for well production equipment is disclosed in U.S. Pat. No. 5,209,300 issued to Ayres. An apparatus and method described in the Ayres '300 patent include a vessel which holds the chemical and a pressurized gas which exerts a pressure on the chemical. A pressure regulator and a valve selectively control the injection of the chemical into the well as the pressurized gas urges the chemical out of the vessel. The pressurized gas drives the chemical through the regulator, valve, and into the well without venting the chemical or pressurized gas into the ambient environment. The apparatus described in the Ayres '300 patent is adapted to inject chemicals into the well in essentially undiluted form. It is also known in the art to use the pressurized chemical treatment tank with an automatically controlled “flush” system that dispenses produced water from the well back into the well when treatment chemical is dispensed from the pressurized tank. See, for example, U.S. Pat. No. 7,721,806 issued to Ayres.